Conventionally, copper particles are prepared by atomization, electrolysis, hydrometallurgy, or solid state reduction processes.
Briefly, atomization includes the steps of melting copper until it is a liquid and flowing the liquid copper through an orifice where it is struck by a high velocity stream of gas or liquid. Typically, this stream is water. The (water) stream breaks the molten metal into particles that then rapidly solidify. In this process, several factors influence the particle size and shape, including: the atomizing medium, the pressure, and the flow rate.
Electrolysis can be used to produce electrolytic copper powder. This process follows the same principles that are used in electroplating, but the conditions are changed to produce a loose powder deposit rather than a smooth solid layer. These conditions include: a low copper ion concentration in the electrolyte, high acid concentration, and high cathode current density. The properties of the copper particle vary depending on, among other variables, the temperature and current density.
In the hydrometallurgy process, copper is leached from cement copper, the solution is then filtered, thus producing copper powder particles. The properties of the copper particles depend on temperature and other process variables.
In the solid state reduction method, copper oxides are ground to a predetermined or desired particle size and then reduced by a gas at a temperature that is below the melting point of copper. The particle size and shape depends on the particle size and shape of the copper oxide, the temperature, the pressure, and the flow rate of the gas.
The above processes all have significant limitations including: too large of a range of particle size distribution, lack of a uniform grain size, and do not have the purity levels required by some applications.